All other rows inbetween the decrease rows are pattern as usual, with no decreasing.

I have knit hundreds of pullovers and cardigans. I still write out my pattern directions, such as I did for you above. I also circle each decrease row# after I have done it, to keep track of where I'm at.
Sometimes it helps to put a stitch marker XX stitches in from each end, to keep track of the declining number of stitches. You will be most likely to forget the decrease at the end of a row. By placing stitch markers to separate the stitches that will be decreased from the main body of stitches, you can easily ascertain if you missed a decrease.

GUIDELINES for pattern reading:
1) When instructions say "dec 1 st each edge on next row"...it means THE NEXT row. That's it.

2) Some armhole shaping has to be done from the RS facing you.
Some armhole shaping for the other side has to be done with the
WS facing you. (as in the case of a Left Front and a Right Front)

That's what patterns mean when they 'shorthand' the pattern for the Right Side Armhole Shaping. Example: do armhole shaping as for the Left Front, reversing the shaping.

Other KH knitters will help us and expand on my post, which is by no means as extensive as it could be.